Neuartige basische Liganden für die homogenkatalytische Methanolcarbonylierung, XXXVIII. Synthese, Eigenschaften und fluktuierendes Verhalten von (Ether‐Phosphan)palladium‐Komplexen

Abstract

Novel Basic Ligands for the Homogeneous Catalytic Carbonylation of Methanol, XXVIII''. -Synthesis, Properties and Fluxional Behavior of (Ether-Ph0sphine)palladium Complexes Cl,Pd(COD) (1) (COD = 1,5-cyclooctadiene) reacts with 1 equiv. of the (ether-phosphine) ligand PhzP-D (2a-c) [D = CH;!C4H70 (a), CH2C4H702 (b), CH2CH20CH3 (c)] to give the dimeric complexes [p-ClPdCl(Ph,P-D)], (3a-c) (P-D = ql-P-coordinated). According to the field-desorption mass spectra which show only one peak for the monomeric moieties C1-Pd(Ph2P-D), 3a-c have a very weak Pd2C12 bridge. trans-Cl,Pd(Ph,P-D), (4a-c) is obtained either from 3a-c and 2a --c by cleaving the PdzClz bridge or from 1 and 2 equiv. of the ligands 2a-c. 4c crystallizes in the monoclinic space group P2,/c with Z = 2. AgC104 selectively abstracts one Cl0 ligand from 4a-c which results in the formation of the cationic complexes [trans-(PhzPnD)(PhzP-D)PdCl]@ (5a-c) (PnD = q'-D,P-coordinated) containing one chelated and one ql-Pbonded (ether-phosphine) ligand. 5a-c show fluxional behavior which is demonstrated by temperature-dependent 31P{ 'H}-NMR investigations. The coalescence points have been determined and are at 253 pa), 303 (5b), and 283 K (54. The activation enthalpies AG' are estimated at 48, 58, and 54 kJ/mol. The abstraction of the second Cl0 ligand from 5a -c succeeds only in the presence of AgSbFs yielding the dicationic bis(che1ate) complexes [trans-(Ph,PnD),Pd]2Q (6ac). The latter are also obtained from 4a-c and AgSbF6. The hydrogenating properties of 3a-c and 4a-c toward 1-hexyne are investigated in comparison with trans-Cl,Pd(Ph,P-CHZCH2CH3)Z.Bei der in homogener Phase durchgefiihrten, Cobalt-katalysierten Hydrocarbonylierung von Methanol zu Acetaldehyd enveisen sich Ether-Phosphane fur eine Erhohung des Methanol-Umsatzes und die Produktselektivitat als au-Derordentlich vorteiIhaft z), Im Gegensatz zum Phosphor-Atom, das den festen Kontakt zum katalytisch aktiven Metallzentrum herstellt, bildet das Sauerstoff-Atom nur schwache und deshalb leicht zu offnende Metallkontakte aus. Die

Changes in Coordination of Sterically Demanding Hybrid Imidazolylphosphine Ligands on Pd(0) and Pd(II)

“…We are aware of only a single recent report on such a process in imidazolylphosphine complexes, however, without data on the activation parameters . There are a few examples in pyrid-2-ylphosphine chemistry of complexes with one chelating and one nonchelating phosphine, some without exchange − and others with some evidence of exchange. − There are examples of other hemilabile Pd complexes, for example ones with pyridylphosphines in which the heterocycle and the phosphine are separated by several atoms, − or complexes with phosphines containing ethers as well as other functional groups , the differences in ligand type or metal preclude any meaningful comparison.…”

“…73 nonchelating phosphine, some without exchange [92][93][94] and others with some evidence of exchange. [95][96][97] There are examples of other hemilabile Pd complexes, for example ones with pyridylphosphines in which the heterocycle and the phosphine are separated by several atoms, [98][99][100] or complexes with phosphines containing ethers 101 as well as other functional groups. 10 However, in most cases activation energies were not reported, or in the cases where this information is available, 99,102 the differences in ligand type or metal preclude any meaningful comparison.…”

Swift and Selective Reduction of Nitroaromatics to Aromatic Amines with Ni–Boride–Silica Catalysts System at Low Temperature

“…To mention a few, Kantam et al [16] reported good conversions at room temperature in reduction of nitro aromatics to their aromatic amines with Pd-MCM(II) catalysts. Han and Jang [17] reported the reduction of nitro aromatics using montmorillonite clay (K-10) with anhydrous hydrazine (1:6 molar ratio) in ethanol under reflux conditions in nitrogen atmosphere for 2 h. Carlini et al [18] investigated many mono [19][20][21] and diphosphine [22][23][24][25][26] modified complexes, such as diphsophine polymer-bound palladium complexes, which can be prepared in few steps, as catalysts, but gave low conversions. Sudalai et al [27] reported hydrogen transfer reaction of nitro aromatics on Ni-zirconia catalysts at reflux temperature, which required the use of stoichiometric amounts of base to enhance the reaction.…”